Summary Cache driver GetBlob() allows read access to any blob without access control check Details If a Zot accessControl policy allows users read access to some repositories but restricts read access to other repositories and dedupe is enabled (it is enabled by default), then an attacker who knows the name of an image and the digest of a blob (that they do not have read access to), they may maliciously read it via a second repository they do have read access to. This allows an attacker to read an image that the accessControl policy denies. This attack is possible because ImageStore.CheckBlob() calls checkCacheBlob() to find the blob a global cache by searching for the digest. If it is found, it is copied to the user requested repository with copyBlob(). This cache behavior is intentionally used in RouteHandler.CreateBlobUpload() to implement cross repository blob mount (POST /v2/<name>/blobs/uploads/?mount=<digest>&from=<repository name>) in Zot. This is still missing an access control to check read access on the source repository. This cache behavior is unexpectedly also used in RouteHandler.CheckBlob() too for HEAD /v2/<name>/blobs/<digest>. If a blob is requested that does not exist on the requested repository, Zot will search for it in a global cache (possibly returning a result from an from an incorrect repository) and then will store it into the ImageStore for the requested repository. RouteHandler.GetBlob() does not call ImageStore.CheckBlob() so it is not directly…Read More